Architecturally Exposed
Structural Steel (AESS)
Custom curtainwall has been the staple of
Enclos Corp that has given us the ability
to assert ourselves as one of the leading facade specialty contractors in North
America. Along with cladding the exterior
of some of the most renowned and expansive buildings, we have also incorporated
storefronts, cable nets, cable walls, and
space frames into our business model.
Now we are seeing owners and architects
investing more time in the design of not
only the main portion of the building, but
also the entrances, pavilions, and skylights
of their projects. As they begin to express
this trend, we too have to accommodate
to meet all the requirements set forth and
position ourselves to continue to lead the
way in all areas of facade design and
installation.
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AESS
Figure 1. LA Live Podium AESS trusses.
As we begin to see this trend take hold,
the most common material used in these
designs is Steel. The efficient use of
structural steel in buildings goes back to
the 17th century. Structural steel is the
backbone of many buildings both small
and large. In the past, it was general
practice to hide the structural steel behind
plaster or drywall to mitigate any imperfections, large connections, or just the raw
look of the material. However, we are
beginning to see more and more architects
use structural steel in their design as an
artistic expression prominently displaying
it for physical viewing. We have come
to know this art form as Architecturally
Exposed Structural Steel (AESS). With
the steel now on display for everyone to
appreciate, Architects want to minimize
the imperfections in steel and be able to
get as close to a perfect product as possible. With minimizing these imperfections,
comes more precise tolerances and higher
quality finishes, resulting in increased labor
and rising costs compared with the typical
structural steel specifications. There are
different levels of AESS acceptability and
standards where if you do not notify your
manufacturer precisely what to fabricate,
your project could have higher costs in
manufacturing than necessary, or possibly not high enough standards resulting
in having to re-fabricate or re-finish the
product. In this paper I will layout what you
need to be aware of when installing AESS,
and list the different tolerances, finishes,
welds, and any other information that may
help you when receiving pricing for any
AESS products.
When receiving construction documents
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that call out AESS where do we begin?
The first place we should familiarize
ourselves with is ASTM A6/A6M, “Standard Specification for General Requirements for Rolled Structural Steel Bars,
Plates, Shapes, and Steel Piling”, along
with this Specification we should review
AISC 303-05, “Code of Standard Practice
for Steel Buildings and Bridges” specifically section 10 on AESS. After we gain a
basic understanding of the specifications
and codes for structural steel we need
to get a feeling for what the architect is
trying to communicate through his/her
design. The AISC (American Institute of
Steel Construction) has created a helpful
matrix to specify techniques that need to
be taken to achieve the different levels of
appearance for AESS. It begins with the
AESS basics cover in section 10 of AISC
303-05, and next moves to the matrix
which they created starting with Category
3, which is “high profile conditions that are
out of reach to touch and can be viewed
from a distance of 20 feet or more”. Next,
Category 2 is “high profile conditions that
are out of reach to touch and can viewed
in close proximity within 20 feet”. Category
1, is the highest level specified as “high
profile conditions that are within reach to
touch and can be viewed in close proximity”. There is also the option where the
user can specify a combination of the 3
noted categories based on their project
requirements.
The most important component in achieving the desired look of AESS is the initial
stage of fabrication. Before fabrication
begins however, you will need to find a
competent fabricator that has previously
performed AESS projects. Just the fact
that they are a steel fabricator will not
qualify them as an AESS fabricator. Truss
Works International, for example, has the
following certifications; City of Los Angeles
Approved Fabricator, ISO 9001 Quality
Systems Certified, Member of AISC, and
has LEED AP green building professionals on staff. Be sure to choose carefully
when you are selecting your fabricator as
this will make or break your project from
the start. Next, you will need to have a full
understanding of each fabrication process
listed in the cost matrix. This is the basic
platform that will help you identify and set
AESS apart from standard structural steel.
In the sections to follow I will talk in more
depth about the fabrication, finishing, and
on-site requirements.
FABRICATION
Now that you have found an appropriate AESS fabricator, you will need to
determine what type of processed steel
you need to purchase, cold formed or hot
rolled. This can be determined by the
shapes required for your project, and how
you can make the required components
out of the typical steel shapes. Keep in
mind that cold formed steel is considerably
most costly than hot formed steel, but often
is more desired by architects due to their
sharp corners. Once you have determined what category of AESS needs to
be provided for your particular project, you
can provide them with the specifications
required for your project. For simplification
of this paper I will begin with discussing
the basic requirements for AESS from
section 10 of AISC 303-05, and work my
way through the matrix categories as the
fabrication requirements increase. To
begin, the basic fabrication requirements
that make AESS different from standard
structural steel are;
• Special Care in Processing AESS –
Upgraded care in process of fabricating,
trucking, handling, storing, and erecting
the material is required to obtain minimally
acceptable AESS.
• Tolerances: One Half Standard – The
tolerances for structural steel frames are
set by AISC Code of Standard Practice. If
AESS is specified, these tolerances are required to be one-half of those of a standard
structural steel.
• Coping and Blocking Tolerances Minimized – Requires that all copes, miters,
and cuts in AESS material are to be made
with a uniform gap of 1/8”
• Joint Gap Tolerance Minimized – A clear
distance between abutting members of
1/8” is required.
• Piece Marks Hidden – AESS pieces are
marked in inconspicuous places whenever
possible, but there are many cases where
these marks are seen. If removal of these
marks is required for aesthetic reasons,
this classification should be specified
• Surface Defects Minimized – In the process of handling the materials, the flanges
of the beams and columns will inevitably
be deformed and scarred. If this classification is specified, these deformities and
scars will be removed.
The above processes provide the basic
fabrication processes required for AESS.
You should be able to describe to the customer that these are the processes they
will receive unless they specify otherwise.
The next level, Category 3, “high profile
conditions that are out of reach to touch
and can be viewed from a distance of 20
feet or more”. The additional requirements
for this category are;
show through is seen on the opposite
side of where the piece was welded. If
required, weld show through is ground by
hand, and may leave a blemish.
• Rolled Members: Minimize Distortion – When rolling members into various
shapes, the member will be distorted.
Distortion must be minimized.
• Close Weld Access Holes at Full Pen
Welds – Weld access holes are holes
in the web of beams and columns to
allow the welder to weld in areas of the
member’s web. If they are required to be
closed for aesthetic reasons, special attention is required in the shop and field.
• Bolt Head Orientation Dictated – Special
attention is required in the shop and the
field for the bolt heads to be orientated in a
particular direction
Category 2, “high profile conditions that are
out of reach to touch and can be viewed in
close proximity within 20 feet”, additional
requirements are as follows;
• Welds Ground Smooth – In standard
structural steel, welds are left in as is
welded condition with slag and weld spatter removed. This is the same for AESS,
however, if it is specified, welds must be
ground smooth
• Welds Contoured and Blended – If
transitions of smoothly grounded welds
are required to be contoured and blended,
this process will be done by hand and will
leave blemishes around the weld area.
Samples should be submitted for review.
• Weld Show Through Minimized – Weld
• Field Welding Aids Removed – Sometimes field welding aids are not removed
due to structural integrity issues. If specified, special attention is required in the
shop and field.
Category 1, “high profile conditions that
are within reach to touch and can be view
in close proximity”, is the highest set standard for AESS. It requires considerably
more work, and also a significant cost increase over standard structural steel. The
requirements, in addition to all previously
listed requirements, are as follows;
• Continuous Welds – Intermittent welds
required for strength, may be required to
be continuous for aesthetic reasons. Special attention is required to avoid distortion
of the member.
• Mill Marks Removed – Steel mill marks
with their heat numbers and producer information identifying the material chemistry
and strength, must be removed.
• Grinding of Sheared Edges – Materials
with sheared edges during the fabrication
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AESS
Figure 2. Different types of fillet welds.
WELDING
There are many different types of welds
and welding processes that may add additional costs to your project. Many of the
typical welding processes are listed in the
fabrication section above. You should be
aware that these processes will add cost
due to additional work being performed.
For example, a typical fillet weld will be left
as is. However, if the fillet weld is called
out to be ground smooth, you have to miter
the steel plate then grind the weld flat adding additional processing time.
We will not go to in-depth regarding the
different welds and so forth as the fabricator should let you know the price per foot
of each type of weld and also why it may
be costing more than another type of weld.
For example, a MIG (Metal Inherent Gas)
Now that you have your steel fabricated,
you are ready to choose the appropriate
finish.
Generally we will not have to concern
ourselves with this step, but in the instance
that our steel is part of the primary structure we will have to apply fireproofing to
the steel between the priming and finishing
steps. There are several different ways
to fireproof steel, but generally the best
way to fireproof AESS to maintain and
not detract from its appearance, is to use
an intumescent paint. This application
differs from job to job, but commonly is
a multi-layered process requiring drying
between each layer. Although it wasn’t in
our scope of work for one of my jobs, there
were structural steel columns requiring
20+ layers of intumescent paint prior to
applying the top coats. So if you have this
condition make a note that you will need to
include plenty of time in your schedule for
the painting process. Also keep in mind
that if there is damage to the intumescent
coating, an extensive patch repair process
must be completed to fix the coating.
http://www.albi.com/ Product - Fireproofing
for Exposed Structural Steel
To begin you must have your steel properly cleaned and prepped before applying
any coating. The platform to start off with
for AESS is “Power Tool Cleaning” (SSPCSP3). This will remove all loose mill scale,
loose rust, loose paint, and other foreign
material. Performing this level of cleaning
will be in combination with (SSPC-SP1)
requiring solvent cleaning prior to using
the power tools. The next level of cleaning
would be (SSPC-SP6) “Commercial Blast
Cleaning”. The definition of this is “…
when viewed without magnification, shall
be free of all visible oil, grease, dust, dirt,
mill scale, rust, coating, oxides, corrosion
products, and other foreign material.” The
difference between the two is a 10%-20%
cost. (You can refer to http://www.sspc.
org/standards/spscopes.html for additional
surface preparations).
GALVANIZING
Galvanizing is a surface protection that
PRIMERS
There are several different types of primers
that can be used for steel; Alkyd, Acrylic,
Epoxy, and Zinc Rich. The first two are
lower end and also cheaper, however,
on our projects we would typically see
either an Epoxy based primer or a Zinc
Rich primer as these are generally used
for higher end coatings. Epoxy Primers
are used for corrosion resistance and hide
small imperfections in the steel as they
have a high build film. A wide variety of
finishes can be used in conjunction with
Epoxy primers. Zinc Rich Primers are
used for superior corrosion resistance, and
have cathodic protection which protects
Figure 3 (left). Cosmetic MIG weld.
Figure 4 (right). Cosmetic TIG weld.
Figure 5 (below). AESS Sample QC Document.
FINISHING
With finishing any material we would like to
keep it in a controlled environment such as
the shop, however you cannot always have
this option. In some conditions, such as
when you have to field weld for the attachment of your steel, you will need to leave
the paint set back so it does not interfere
with the welding process. Make a note of
these conditions when choosing a finish
type. The architect should call out the type
of finish and color he would like to use,
but again check with your applicator to
make sure the finish is compatible with the
primer and will work for the applications
required to cure and apply the finish. Similar to the primers, the finishes also have
the option of Alkyds, Acrylics, Epoxies,
and Polyurethanes. Again the first two are
cheaper and instead we will generally see
Epoxy and Polyurethane finishes called out
in our specifications. Epoxies will cover
up imperfections much like the primer, and
are good for high traffic areas where abrasion resistance is required. Epoxies are
not to be used for exterior applications as
they will chalk when exposed to UV rays;
this is where you would see Polyurethanes
specified, for exterior applications. They
too will cover up minor imperfections in
steel. These should be sprayed applied for
best appearance.
QUALITY PLAN CHECKLIST - STEEL FABRICATION
NEWSEUM GL-1D - BIG WINDOW Job# 2004-158
Completed
Characteristic or Item
Sample Parts
Painted welded steel sample
Design,
Target &
Tolerance
Reference
Steel Structures
Paint Council
(SSPC)
Material Certifications & Testing Requirements
ASTM A36
Steel Plates
(Fy=36ksi,
Fu=58ksi)
ASTM A572 Grade
Steel Bar
50 (Fy=50ksi,
Fu=65ksi)
Welding
Structural Bolts
Threaded Rods
Tube Steel
Shop Welding
Visual Inspection
E70XX Rod
(Fu=70ksi min)
ASTM A325 N
(Fy=92ksi,
Fu=120ksi)
ASTM A449
(Fy=58ksi,
Fu=90ksi)
ASTM A500 Grade
B (Fy=46ksi,
Fu=58ksi)
Per AWS D1.1
Ultrasonic Inspection
ASTM E164
MAG Particle Testing
ASTM E709
Welders Qualification
Per AWS D1.1
Welding Procedures
Per AWS D1.1
Test and
Sample
Reportin
Size
g
and
Method Frequency
5 each
F
A
B
Mill Certs
for all
items
are to be
submitted
to ASI for
review
prior to
delivery to
fabricator
or field
site.
Prior to each
Shipment
F
A
B
F
A
B
F
A
B
F
A
B
F
A
B
F
A
B
Verification
Reports
(In Shop
Fabricator
QC's
Possessio
n for
Review
by ASI)
100% of All
Welds
25% of
Penetration
Welds
25% of Fillet
Welds
Prior to
Fabrication
100% of All
Welds
Verification
Reports
(In Shop
Fabricator
QC's
Possessio
n for
Review
by ASI)
Shop
Fabricator to
Perform
Dimension
Check on
100%
of the Items.
ASI to Review
Submittals &
Perform
Intermittent
Check in the
Shop
(10% of Total
Package).
Visual
Verification
to be
documente
d and
submitted
to ASIC
prior to
shipment.
Shop
Fabricator to
Perform
Visual Check
on 100% of
the Items.
ASI to do
Intermittent
Check
ASI / Client
Approval
Dimensional Checking
(Carbon Steel Vertical
Members)
All Vertical Tubes
All Horizontal Tubes
Critical Dimensions (pin-to-pin)
Balance of Dimensions
All shall be within +/1/8"
at its overall pin-topin length.
Per ASI Design &
Fabricator's Shop
Dwgs,
Latest Revision
Identification, Painting &
Shipment
Piece Mark Identification
Number
(All Parts)
Primer & Finish Coats
All Shop Fabricated Items
Delivered to Site
Quantity Check
Per ASI Design &
Fabricator's Shop
Dwgs,
Latest Revision
Per Project
Specification
Package and
Protect Members
to Avoid Damage
During Shipment.
Shipping Method
Details are to be
Submitted to ASI.
Total of items for
project are to be in
accordance with the
Bill of Materials
reflected on
Fabrication Dwgs,
latest revision.
Visual
Packing
Verification
Prior to
Shipment
(digital
photos)
Shipper's
bill of
lading from
the
fabricator
to be sent
to ASI for
review with
project Bill
of Material.
Design
Review
Provisional
*Reminder* - Steel cannot easily be welded after it has been hot dipped galvanized.
If you do weld hot dipped galvanized steel,
it is extremely expensive and hazardous,
and you will have to apply a cold galvanized spray over the top of the weld to seal
it from the weather.
FIREPROOFING
SURFACE PREP
http://www.haifire.com/magazine/AESS.
pdf Article - “Fire Protection Materials for
Architecturally Exposed Structural Steel
(AESS)
Received
the steel galvanically. They can be specified as organic or inorganic which meet
the requirements for class B slip coefficient
for bolted connection. Keep in mind there
is a longer curing time for the inorganic
primer and you will need a minimum relive
humidity of 40% for the primer to dry. It
would best suit you to contact your paint
applicator to discuss what type of primer
to use in conjunction with the finish coating specified. Also find out if there are
any non-conformances that may result
between the primer and top coat.
Reject
All the above fabrication classifications are
the most commonly referred to requirements. There may be other requests desired by the customer, at which point you
will have to discuss with your fabricator if
they can provide the additional requests
and at what price. This should give you
a good stepping stone on where to start
and how to price the fabrication for your
project.
adds a thin layer of metal (usually zinc)
over the steel to protect the steel from
rusting. You would generally only need to
galvanize the steel if it is to be used in an
exterior application. A common practice
for galvanization is hot dip galvanizing,
where the steel is dipped into a tank and
an electrochemical process occurs resulting in a layer of zinc to be deposited to the
steel surface. Note that this will affect the
surface of the steel making it less uniform
or “rough”. There are ways to smooth the
surface such as sand blasting, but the surface will not be 100% smooth, and this will
also be an added cost to the project.
Accept
• Seal Welds to Close Open Gaps –
Frames may require welds to seal gaps
from environmental implications or aesthetic reasons. Note that this may cause
distortion.
Weld versus a TIG (Tungsten Inherent
Gas) Weld can have significant cost and
time implications. A 12” cosmetic MIG
weld will take 10 minutes to complete,
where as a cosmetic TIG weld of the same
length will take about 45 minutes to complete, resulting in a higher time and cost
impacts. So be very aware of what the
customer is suggesting, and have a V.E.
solution in your back pocket.
Provided By
process may demand that rough surfaces
be deburred and ground smooth
FA
B
FA
B
FA
B
FA
B
FA
B
FA
B
FA
B
FA
B
FA
B
FA
B
FA
B
100%
Verification
Prior to
Shipment
FA
B
100%
Verification
Prior to
Shipment
FA
B
86
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AESS
Figure 6. Steel finish sample showing cut back
layers starting with raw steel (Bottom), 1st layer
primer, 2nd layer primer, finish coat (Top). Also
an example of how to apply step back paint process for field welding and later paint blending.
PAINTING AND FINISHING ISSUES
When finishing steel components we generally will come across the same problems
that we would with aluminum finishes.
Listed below are some basic issues that
you should plan ahead of time so you don’t
get in a bind later:
• Allow for proper drying time
o Many times we do not anticipate drying
time into our schedule resulting in
packaging and shipping while paint is
still “tacky” or wet. This can result in
unnecessary touch-up later in the field
• Finish samples
o Remember to tell the paint applicator
that the samples they provide must
look identical to their finished product
• Many times they will send the best
samples possible on the best
pieces of steel. Try to get them to
mock-up “actual” steel and paint
samples so the architect will not
expect something that cannot
actually be provided
• Touch up samples
o Provide touch up samples that will
simulate field condition touch-ups
• This is critical to your project, as
field touch-up will never look as
good as the factory applied paint
• Applicator/Paint Representative visit
o It is a good idea to have the paint rep
come and inspect painted members to:
• Review the Process
• Ensure proper mil thickness
• Quality
88
• Approve the vendor that is applying
the paint
QUALITY CONTROL
Prior to any work being started your team
should have a QC plan already thought out
and being devised. One major mistake is
starting any fabrication without standards
being set in place. A sample QC sheet
is included in this paper for reference.
Although this QC sheet is a good place to
start, every project has different conditions
that need to be projected prior to beginning
your project. You should have QC plans
for both the shop and the field. Another
large component of the QC process is
packaging and handling. The overall QC
process should be similar to our curtainwall
QC process as the majority of the work is
done up-front in the shop, and we do not
want to go back and make any field adjustments or touch-ups.
In shop QC
Review the specs to see if there are any
testing procedures that need to be done on
the steel. Make sure you allow time for the
tests to be completed and also if any steel
needs to be re-fabricated or re-purchased.
Be sure to get your mill certificates from
your suppliers as well. You should check
the steel at the shop periodically during
fabrication. Prior to finishing you should
check all dimensions. Have your engineer
create a set of check drawings that include
check dimensions and geometric dimensions. This will help you ensure that all the
holes, connections, and components are
in place so you will not have to make any
modifications or adjustments in the field.
Once the steel is verified it can be sent for
paint. Paint again should be compared
to the submitted sample and should be
uniform. Also make sure it has had the
allotted drying time prior to packaging.
Packaging is also a very critical, but often
an overlooked step. First and foremost,
make sure everything is well protected.
Next, the steel components are usually
large and may need a rack to be fabricated for their shipping alone. The steel
cannot bend in any way as it may deform
in the short time it is being transported,
resulting in difficulty making your connections upon installation.
One other issue that you should be aware
of, but may not be a factor on every job,
is built up tension in the steel due to
welding. This is caused by extensive
welding and heating of the steel causing
the molecules to stress and re-align. The
problem is usually seen after the steel is
shipped to site, as it vibrates on the road
and relaxes back to its original state causing the steel to bend or bow. There are
two ways to alleviate this stress. One is
to vibrate the steel in the shop to relax the
molecules allowing you to make adjustments in the shop. The other is to heat
up the steel, then uniformly cool it to relax
the steel gradually.
If you have taken all these precautions,
your steel should arrive in good shape
and be ready for installation.
In Field QC
Prior to any material arriving on site, you
must complete your site survey. Make
sure all other trades work (concrete,
primary steel, drywall, etc) is in tolerance to ensure the most accurate fit of
all your components. You cannot count
on all trades to have their product 100%
accurate, and also their tolerances are not
as tight as AESS. One way to accommodate for their tolerances is to make all
your anchors the same, and field cut them.
When we did this at LA Live it ensured that
our trusses were aligned all the way down
the wall and we did not have to try to accommodate to the other trades work. The
negative side to this was we had to field
cut the anchors, and do paint touch-up on
the cut areas. There are definite trade-offs
involved either way you go, you just have
to weigh out your options and choose the
best one. If you choose to go off their
installed components and you find anything to be out of tolerance, notify the GC
immediately so the trade responsible can
make accommodations without affecting
your schedule. After installation, all you
should have to do is inspect your work to
make sure no damage has occurred during
shipping or installation. Note the damage
that has occurred during shipping and
installation, and complete the floor-by-floor
sign off so if any damage occurs in the
future it will be noted as trade damage.
INSTALLATION
Once you have reached this point, all the
hard work and planning should have been
done so all you have to do is install the
AESS components. Having a solid field
plan on how you will erect the steel is es-
sential. The type of equipment you are
going to use should be well thought out,
and also how you are going to hoist the
material without it deflecting or bowing
should be carefully reviewed. In the rare
occurrence that a component will not
align, or something is out of tolerance and
does not fit properly, you should have
back up plans set in place. This will ensure no delays and keep your men working without interruption. There are always
disruptions and problems that occur to
even the most well thought out plan, so
expect some hiccups along the way, but
if all your pre-planning is set in place the
installation should go fairly smooth.
BIBLIOGRAPHY
“AESS_Spec.pdf.” AISC | Home. Modern Steel
Construction, May 2003. Web. 06 June 2010.
<http://www.aisc.org/WorkArea/showcontent.
aspx?id=17506>.
American Institute of Steel Construction 303-05
Section 10
Parker, Aurther J., Jesse J. Beitel, and Nestor
R. Iwankiw. ““Fire Protection Materials for Architecturally Exposed Structural Steel (AESS)”.”
Hughes Associates, Inc. - Fire Protection Engineers, Fire Protection Consultants, Fire Investigators – Leaders in Fire Testing, Fire Modeling,
Fire Protection Design. Http://www.haifire.com/
Architecturally Exposed Structural Steel
is finding a place in more and more
construction projects and is here to stay.
With our current facade knowledge, and
our desire to take on more complex and
architecturally appealing projects, we find
the need to familiarize ourselves with this
intricate material. This paper was written
for you to gain an understanding of the
basic intricacies involved with AESS and
give you some resources where you
can go find more information for your specific job. I only wrote in-depth regarding
AESS and did not discuss stainless steel,
extruding steel, castings, or metal spinning which all could have a large section
devoted to each topic. Shortly after this
paper is written, we will begin producing AESS sample boards that will be
distributed to several of the main offices
throughout Enclos. These, in addition to
the paper, will help you grasp the general
concepts involved with AESS fabrication
and finishing.
magazine/AESS.pdf, Feb. 2005. Web. 06 June
2010. <http://www.haifire.com>.
Untitled Document. Web. 06 June 2010. <http://
www.sspc.org/standards/spscopes.html>.
REFERENCES
American Institute of Steel Construction
AISC 303-05
American Society for Testing of Materials
ASTM A6/A6M
American Welding Society
AWS_D1.1_2006
Albi (Fireproofing supplier)
The Society for Protective Coatings
AESS Sample QC Document (below)
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